In the design of semiconductor devices, it is often desired to analyze current flow through various circuits. Such analysis is particularly beneficial with respect to integrated circuits to isolate points of potential failure. One method of analysis takes advantage of the electroluminescent characteristics of silicon.
Avalanche breakdown can be analyzed by observing emitted light. The light is emitted as a result of the electroluminesence of silicon avalanche. Thus, light emission in this situation enables the detection and location of areas of current flow.
Oxide defects can be detected by observing the light emitted upon application of a current. By observing the emitted light, the points of failure of a damaged product can be determined, and an analysis of design flaws and/or processing flaws can be advantageously undertaken.
Finally, the profile and detailed effects of an ESD (electrostatic discharge) event in an integrated circuit may be determined. During ESD, p-n junctions become forward biased or even go into avalanche breakdown. In either case, light is emitted. By profiling the emitted light pattern, the profile of the ESD event can be observed and the area of dissipation of the ESD energy determined.
In the past, the light emitted from IC devices has been observed through the use of time exposure photography. Typically, a double exposure is made so that the emitted light can be associated with a particular structure or device of the circuit.
A disadvantage with time exposure photography is the inability to isolate time as a factor in the light emission. Typically, time exposure photographs are taken with the device in a steady state condition; however, many failure mechanisms can only be observed in the transient state, such as the hot electron effect in inverters. Inverters typically are subject to hot electron degradation when switching staes. Thus, the timing of the switching transition is important to determine the occurrence of hot electron degradation.
Another past method of observing light emission from IC devices is the use of an infrared or optical microscope. However, these microscopes suffer from an inability to detect faint emission levels. Thus, faint emission of light, or subtle contrasts of emitted light, are often undetectable. Again in these approaches it is not possible to resolve time varying light emission effects.
The amount of light transmitted through a lens is proportional to:
(N.A).sup.2 /(MAG)
when NA is the numerical aperature and MAG is the magnification of the lens.
However, there are no commercially available lenses with sufficiently high numerical aperature and low magnification to maximize brightness. Thus, the application of optical microscopes for analysis of the electroluminesence of silicon is limited.
Therefore, it is an object of the present invention to provide an emission microscope which allows stroboscopic observation of extremely faint emitted light from silicon devices in a short period of time.
It is a further object of the present invention to provide an emission microscope which can detect faint emissions of light and small contrasts of emitted light.